The present invention relates to a coma aberration automatic measuring mark used for measuring only a coma aberration of various aberrations of a lens system used in a reduction projection exposure, and a method for measuring the coma aberration by using the coma aberration automatic measuring mark.
One important factor is to quickly and simply measure a coma aberration of a reduction projection lens system. Now, a prior art method for measuring the coma aberration of the reduction projection lens system will be described with reference to FIGS. 1A and 1B.
As shown in FIG. 1A, a prior art coma aberration automatic measuring mark is constituted of a plurality of strip-shaped patterns L1 L2, L3, L4 and L5 arranged in parallel to one another and separately from one another, at a pitch which is about a double of a wavelength of an exposure light. A line width of a projected pattern of each of the strip-shaped patterns L1, L2, L3. L4 and L5 is measured by for example a length measuring SEM (scanning electron microscope), and the amount of coma aberration is calculated from a difference in the line width between the strip-shaped patterns L1 and L5 positioned at opposite side ends of the projected coma aberration automatic measuring mark, as shown in FIGS. 1A and 1B.
FIG. 1A illustrates a case having no coma aberration, and FIG. 1B illustrates a case having a coma aberration. FIG. 1C illustrates a case having a spherical aberration.
In the prior art, however, when the coma aberration is very large, it is not possible to carry out an automatic measurement utilizing an image processing, and therefore, the coma aberration must be measured manually, with the result that the measurement needs a considerable time. Therefore, adjustment of the reduction projection lens system cannot be smoothly performed, and a satisfactory degree of reproduction cannot be obtained because of the manual measurement. In addition, it is difficult to separate the coma aberration from the other aberrations occurring in the reduction projection lens system.